Bonding structures and methods of forming the same

ABSTRACT

A package includes a package component and a second package component. A first elongated bond pad is at a surface of the first package component, wherein the first elongated bond pad has a first length in a first longitudinal direction, and a first width smaller than the first length. A second elongated bond pad is at a surface of the second package component. The second elongated bond pad is bonded to the first elongated bond pad. The second elongated bond pad has a second length in a second longitudinal direction, and a second width smaller than the second width. The second longitudinal direction is un-parallel to the first longitudinal direction.

BACKGROUND

Metal-to-metal bonding (also sometimes referred to as direct bonding) isa commonly used bonding method in the packaging of integrated circuits.In the direct bonding, the bond pads of two wafers or chips are bondedtogether without solder disposed in between. For example, the directbonding may be a copper-to-copper bonding or a gold-to-gold bonding. Themethods for performing the direct bonding include Thermal CompressionBonding (TCB, sometimes known as thermal compressive bonding). In atypical direct bonding process, the metal bumps of a device die arealigned to, and are placed against, the metal bumps of a packagesubstrate. A pressure is applied to press the device die and the packagesubstrate against each other. During the bonding process, the device dieand the package substrate are also heated. With the pressure and theelevated temperature, the surface portions of the metal bumps of thedevice die and the package substrate inter-diffuse, so that bonds areformed.

The direct bonding typically requires large metal pads. The large metalpads, however, may incur severe dishing problem in the planarization ofthe metal pads. Furthermore, Misalignment between the two bonded packagecomponents may occur, and hence the contact area of the bonds may varydepending on the severity of the misalignment. The variation of thecontact area results in the variation of the contact resistance, whichin turn results in the variation in the performance of the resultingpackage. When the metal-to-metal bonding is used to bond integratedcircuits that have high bond densities, due to the small sizes and thesmall pitches of the bond pads, the variation in the contact resistanceis worsened.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 schematically illustrates the bonding of two package componentsin accordance with exemplary embodiments, wherein the bonding isperformed through metal-to-metal bonding;

FIG. 2 illustrates a top view of the bond pads at a surface of a firstpackage component in accordance with exemplary embodiments, wherein bondpads are laid out with a staggered layout, and are located on one sideof an array;

FIG. 3 illustrates a top view of the bond pads at a surface of a secondpackage component, wherein the bond pads of the second package componentare to be bonded to the bond pads of the first package component shownin FIG. 2;

FIG. 4 illustrates a top view of the bond pads at a surface of a firstpackage component in accordance with alternative exemplary embodiments,wherein the bond pads are located on opposite sides of an array;

FIG. 5 illustrates a top view of the bond pads at a surface of a secondpackage component, wherein the bond pads of the second package componentare to be bonded to the bond pads of the first package component in FIG.4;

FIG. 6 illustrates a top view of the bond pads at a surface of a firstpackage component in accordance with yet alternative exemplaryembodiments, wherein the bond pads are staggered, and are located onopposite sides of an array;

FIG. 7 illustrates a top view of the bond pads at a surface of a secondpackage component, wherein the bond pads of the second package componentare to be bonded to the bond pads of the first package component in FIG.6;

FIG. 8 illustrates a top view of bond pads in accordance with someexemplary embodiments, wherein elongated bonds pads of a same wafer orchip have longitudinal directions un-parallel to each other;

FIG. 9 illustrates a top view of bond pads in accordance with someexemplary embodiments, wherein bonds pads in same bonded pairs havelongitudinal directions neither perpendicular to each other nor parallelto each other; and

FIG. 10 illustrates a cross-sectional view of two bond pads that arebonded to each other.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable concepts that can be embodied in a wide varietyof specific contexts. The specific embodiments discussed areillustrative, and do not limit the scope of the disclosure.

A bond structure is provided in accordance with various exemplaryembodiments. The variations of the embodiments are discussed. Throughoutthe various views and illustrative embodiments, like reference numbersare used to designate like elements.

Referring to FIG. 1, package component 200 is bonded to packagecomponent 100 through metal-to-metal bonding, for example, which is alsoreferred to as direct bonding. In alternative embodiments, other bondingmechanisms such as solder bonding can be used. In the bonding process,elongated bond pads 108 (FIGS. 2 through 10) on the surface of packagecomponent 100 are in physical contact with, and are bonded to, theelongated bond pads 208 (FIGS. 2 through 10) of package component 200directly, wherein no solder is applied between elongated bond pads 108and their corresponding elongated bond pads 208. During the bondingprocess, package components 100 and 200 may be heated, and a pressuremay be applied to press package components 100 and 200 against eachother. With the pressure and the elevated temperature, the surfaceportions of bond pads 108 and 208 inter-diffuse, so that bonds areformed.

In accordance with some embodiments, each of package components 100 and200 may be a device wafer, an interposer wafer, a package substratestrip, or the like. In the embodiments wherein package components 100and 200 are device wafers, package components 100 and 200 may be logiccircuit wafers, memory wafers, Complementary Metal-Oxide-Semiconductor(CMOS) Image Sensor (CIS) wafers, or the like. For example, in theembodiments wherein package components 100 and 200 are memory wafers,package components 100 and 200, after bonded, form stacked memories. Inthe embodiments wherein package components 100 and 200 are CIS wafers,package components 100 and 200, after bonded, form 3D-CIS packages. Inthe embodiments wherein package components 100 and 200 are interposerwafers, package components 100 and 200 are free from active devices suchas transistors therein, and are used to route electrical connectionsfrom one side of the interposer wafer to the opposite side. In theembodiments wherein package components 100 and 200 are package substratestrips, package components 100 and 200 may include a plurality ofpackage substrates, and may include build-up substrates (with cores) orlaminate substrates. Although FIG. 1 illustrates that package components100 and 200 have round top-view shapes, they may also have rectangulartop-view shapes. Furthermore, in some embodiments, each of packagecomponents 100 and 200 may include a plurality of chips therein.Alternatively, each of package components 100 and 200 may be a discretedevice die, a discrete package substrate, a discrete interposer die, orthe like, which have already been sawed from the respective wafer orstrip at the time it is bonded.

FIG. 2 illustrates a top view of package component 100, and thecomponents in package component 100. In the embodiments packagecomponent is a wafer, package component 100 may include a plurality ofdies (with one die 102 illustrated) identical to each other. In thepresent disclosure, image sensor arrays 104 and the correspondingconnection lines 106 and elongated bond pads 108 are used as examples toexplain the concept of the embodiments. It is appreciated that theteaching of the embodiments also applies to all other types of circuitssuch as memory arrays, logic circuits, and the like.

In some exemplary embodiments, package component 100 includes imagesensor array 104, which includes a plurality of image sensors (cells)105 arranged as a plurality of rows and columns. In some embodiments,image sensors 105 in each of the columns are connected to one ofconnection lines 106 (including 106A and 106B). Each of connection lines106 may be connected to one of elongated bond pads 108, which include108A and 108B. Connection lines 106 may be in a same metal layer as, andformed simultaneously as, bond pads 108. Alternatively, connection lines106 may be in a different metal layer than bond pads 108. Elongated bondpads 108 are located at a surface of package component 100. The pitch ofthe columns is denoted as P.

Elongated bond pads 108 have length L1 and width W1 smaller than lengthL1. In some embodiments, elongated bond pads 108 have a top-view shapeof rectangles, which may have substantially sharp corners or roundedcorners. Elongated bond pads 108 on the manufactured dies or wafers mayhave rounded corners due to optical effects. The elongated bond pads 108with rounded corners, however, may still include a middle section thatincludes a majority of the respective bond pads, wherein the middlesection has a uniform width W1. Ratio L1/W1 may be greater than 2 orgreater than 3, although smaller ratios may also be used. Ratio L1/W1may also be between about 2 and about 4. In the illustrated embodiments,the longitudinal directions of elongated bond pads 108 are parallel tothe column direction (the Y direction). In alternative embodiments, thelongitudinal directions of elongated bond pads 108 may also be parallelto the row direction (the X direction).

In accordance with some embodiments, the layout of elongated bond pads108 and connection lines 106 have a staggered design, for example, withelongated bond pads 108A aligned as a first row extending in the Xdirection, and elongated bond pads 108B aligned as a second row parallelto the first row. The connection lines 106A that are connected toelongated bond pads 108A are shorter than connection lines 106B that areconnected to elongated bond pads 108B. Furthermore, connection lines106A and connection lines 106B are allocated with an alternating layout.Through this design, elongated bond pads 108A may have their pitchesequal to 2P, and elongated bond pads 108B may also have their pitchesequal to 2P. Through the staggered layout design, elongated bond pads108 are suitable to be used to connect to array 104 that has a smallerpitch, which may be a half of the pitch of elongated bond pads 108A (or108B). Although not shown, in alternative embodiments, all elongatedbond pads 108 may also be aligned as one row, and hence the pitches ofelongated bond pads 108 are also equal to pitch P. The respective designmay be used when pitch P is great enough for accommodating elongatedbond pads 108 and 208.

FIG. 2 also illustrates elongated bond pads 208 that are bonded toelongated bond pads 108. Throughout the description, a bond pad 108 andthe bond pad 208 bonded to the bond pad 108 in combination are referredto as a bonded pair. Elongated bond pads 208 are shown using dashedlines since they are located in package component 200, whose top view isshown in FIG. 3. Referring to FIG. 3, elongated bond pads 208 arelocated at a surface of package component 200, and are bonded toelongated bond pads 108, for example, through metal-to-metal bonding,although other bonding methods such as solder bonding may be used. Inthe embodiments wherein the solder bonding is performed, a solder layermay be formed on each or one of elongated bond pads 108 and 208 that arein the same bonded pair. Elongated bond pads 208 have length L2 andwidth W2 smaller than length L2. In some embodiments, length L2 is equalto length L1 of elongated bond pads 108. In alternative embodiments,length L2 is greater than or smaller than length L1. Furthermore, widthW2 is equal to width W1 of elongated bond pads 108 in some embodiments.In alternative embodiments, width W2 is greater than or smaller thanwidth W1. In some exemplary embodiments, package component 200 includescircuit 204, and connection lines 206 electrically coupling elongatedbond pads 208 to circuit 204. In alternative embodiments, connectionlines 206 route the connection to an opposite surface of packagecomponent 200, which opposite surface is opposite to the surface thatpackage component 100 is bonded to. In the respective embodiments,package component 200 may include an interposer or a package substrate,although package component may also be a device die/wafer includingthrough vias. Elongated bond pads 108 are also illustrated in FIG. 3,and are shown using dashed lines since they are located in packagecomponent 100.

In FIGS. 2 and 3, the longitudinal directions of elongated bond pads 108are un-parallel to the longitudinal directions of elongated bond pads208. In some embodiments, the longitudinal directions of elongated bondpads 108 are perpendicular to the longitudinal directions of elongatedbond pads 208. Hence, when bonded, the contact area between bond pads108 and 208 in the same bonded pair is equal to W1×W2. In the bondingprocess, misalignment between package components 100 and 200 may occur,and the centers of elongated bond pads 108 may be misaligned with thecenters of the corresponding elongated bond pads 208. Advantageously,with the elongated design, even if the misalign occurs, the contact areamay still remain to be W1×W2. The contact resistance thus remainsconstant regardless of whether the misalignment occurs or not, andregardless of the magnitude of the misalignment. To ensure that thecontact area remains to be W1×W2, the lengths L1 and L2 are selected sothat the extended length LE on each side of the intended contact area(the center regions of 108 and 208) is greater than or equal to themaximum alignment of the alignment tool and the alignment process.Alternatively stated, with the extend LE added to each side of theintended contact area, even if the misalignment is maximized in asuccessful alignment operation, the contact area will still be W1×W2.

In the embodiments wherein each of package components 100 and 200includes a plurality of dies, after the bonding process, the bondedstructure may be sawed into a plurality of packages, with each of thepackages including one of dies 102 (FIGS. 2) and 202 (FIG. 3).

FIGS. 4 through 9 illustrate package components 100 and 200 inaccordance with alternative embodiments. Unless specified otherwise, thelayout and the shape of the components in these embodiments areessentially the same as the like components, which are denoted by likereference numerals in the embodiments shown in FIGS. 2 and 3. Thedetails regarding the components shown in FIGS. 4 through 9 may thus befound in the discussion of the embodiment shown in FIGS. 2 through 3.

FIG. 4 illustrates a top view of package component 100 in accordancewith alternative embodiments. These embodiments are similar to theembodiments in FIG. 2, except that elongated bond pads 108 aredistributed on the opposite sides of array 104. Accordingly, the pitchbetween neighboring elongated bond pads 108 is also equal to 2P. Oneadvantageous feature of this layout is that all connection lines 106 mayhave the same length, and hence the same resistance. Elongated bond pads208 are shown in FIG. 4 using dashed lines since they are located inpackage component 100.

FIG. 5 illustrates a top view of package component 200 in accordancewith some exemplary embodiments, wherein package component 200 is bondedto package component 100 in FIG. 4. Elongated bond pads 208 are bondedto bond pads 108 with a one-to-one correspondence. Again, thelongitudinal directions of bond pads 108 may be un-parallel to, and maybe perpendicular to, the longitudinal directions of the correspondingbond pads 208. Elongated bond pads 108 are shown in FIG. 5 using dashedlines since they are located in package component 200.

FIG. 6 illustrates a top view of package component 100 in accordancewith yet alternative embodiments. These embodiments are similar to theembodiments in FIGS. 2 and 3, except that elongated bond pads 108 aredistributed on the opposite sides of array 104. Furthermore, on eachside of array 104, elongated bond pads 108 have a staggered layout. Oneach side of array 104, connection lines 106A and 106B may thus havedifferent lengths, and bond pads 108A and bond pads 108B may be alignedas different rows that are parallel to each other. The pitch betweenneighboring elongated bond pads 108 in accordance with these embodimentsis increased to 4P.

FIG. 7 illustrates a top view of package component 200 in accordancewith some exemplary embodiments, wherein package component 200 is bondedto package component 100 in FIG. 6. Bond pads 208 are bonded to bondpads 108 with a one-to-one correspondence. Again, the longitudinaldirections of bond pads 108 may be un-parallel to, and may beperpendicular to, the longitudinal directions of the corresponding bondpads 208. Elongated bond pads 108A and 108B are shown in FIG. 7 usingdashed lines since they are located in package component 200.

FIG. 8 illustrates that elongated bond pads 108 in a same chip (and/or asame wafer) may have a plurality of longitudinal directions that is notparallel to each other. In accordance with some embodiments, as shown inFIG. 8, some of elongated bond pads 108 have longitudinal directions inthe X direction, and some other elongated bond pads 108 havelongitudinal directions in the Y direction. The longitudinal directionsof elongated bond pads 208 are designed to be un-parallel to thelongitudinal directions of the respective connecting elongated bond pads108. Being able to allocate the longitudinal directions of elongatedbond pads 108 in different directions provides a flexible design forallocating the bond pads, so that the usage of chip area may bemaximized.

FIG. 9 illustrates that elongated bond pads 108 and 208 in the samebonded pair have longitudinal directions un-perpendicular to each other,and un-parallel to each other. Angle a between the longitudinaldirections of elongated bond pads 108 and 208 may be between about 30degrees and 90 degrees. Again, in these embodiments, elongated bond pads108 in the same die or wafer may have a plurality of longitudinaldirections that are not parallel to each other, and elongated bond pads208 in the same die or wafer may have a plurality of longitudinaldirections that are not parallel to each other.

FIG. 10 illustrates a cross-sectional view of a bonded pair includingone bond pad 108 and one bond pad 208, which are bonded to each other.The cross-sectional view may be obtained from any of FIGS. 1 through 9.In some embodiments, dielectric diffusion barriers 110 and 210 areformed on the top surfaces of package components 100 and 200,respectively, and are used to prevent the materials (such as copper) inelongated bond pads 108 and 208 to diffuse to the other packagecomponent. Diffusion barriers 110 and 210 may include nitrides,oxynitrides, or the like. In some embodiments, diffusion barriers 110and 210 may also be bonded to each other, for example, through fusionbonding. The surface of bond pad 208 facing package component 100includes a first portion(s) in contact with a surface of dielectricbarrier 110, and a second portion in contact with and bond to a surfaceof bond pad 108. Similarly, a surface of bond pad 108 facing packagecomponent 200 includes a first portion(s) in contact with a surface ofdielectric barrier 210, and a second portion in contact with and bond toa surface of bond pad 208.

In the embodiments of the present disclosure, the widths of bond padsare reduced, resulting in the reduction of the areas of the bond pads.Accordingly, the dishing effect in the planarization of the bond pads isalleviated, and the bond quality may be improved. Furthermore, with theelongated design of the bond pads and the un-parallel allocation of thebond pads in the same bond pairs, the contact area of the bonds mayremain unchanged even if misalignment occurs.

In accordance with some embodiments, a package includes a packagecomponent and a second package component. A first elongated bond pad isat a surface of the first package component, wherein the first elongatedbond pad has a first length in a first longitudinal direction, and afirst width smaller than the first length. A second elongated bond padis at a surface of the second package component. The second elongatedbond pad is bonded to the first elongated bond pad. The second elongatedbond pad has a second length in a second longitudinal direction, and asecond width smaller than the second width. The second longitudinaldirection is un-parallel to the first longitudinal direction. A ratio ofthe first length to the first width may be greater than about 2.

In accordance with other embodiments, a package includes a die, whichincludes an array of cells, and a first plurality of elongated bond padsat a surface of the die. Each of the first plurality of elongated bondpads is electrically coupled to one column of the cells in the array.The first plurality of elongated bond pads has first longitudinaldirections parallel to each other. The package further includes apackage component, which includes a second plurality of elongated bondpads at a surface of the package component. Each of the second elongatedbond pads is bonded to one of the first plurality of elongated bondpads. The second plurality of elongated bond pads has secondlongitudinal directions parallel to each other, wherein the secondlongitudinal directions is un-parallel to the first longitudinaldirections.

In accordance with yet other embodiments, a package includes a first dieand a first bond pad at a surface of the first die, wherein the firstbond pad has a substantially rectangular top-view shape. The rectangulartop-view shape has a first length extending in a first direction, and afirst width smaller than the first length. The package further includesa second die bonded to the first die, and a second bond pad at a surfaceof the second die and bonded to the first bond pad. The second bond padhas a second length extending in a second direction perpendicular to thefirst direction, and a second width smaller than the second length. Aratio of the first length to the first width may be greater than about2.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A package comprising: a first package component;a first elongated bond pad at a surface of the first package component,wherein the first elongated bond pad has a first length in a firstlongitudinal direction, and a first width smaller than the first length;a second package component; and a second elongated bond pad at a surfaceof the second package component and bonded to the first elongated bondpad, wherein the second elongated bond pad has a second length in asecond longitudinal direction, and a second width smaller than thesecond length, and wherein the second longitudinal direction isun-parallel to the first longitudinal direction, and the firstlongitudinal direction and the second longitudinal direction areparallel to the surface of the first package component, wherein thefirst elongated bond pad and the second elongated bond pad are bondedthrough metal-to-metal bonding, and wherein the first elongated bond padcomprises a first surface comprising a first portion and a secondportion, and the second elongated bond pad comprises a second surfacecomprising a third portion and a fourth portion, with the first portionbonded to the third portion, and the second portion not bonded to thesecond elongated bond pad, and the fourth portion not bonded to thefirst elongated bond pad, wherein the first and the second surfaces havea contact area comprising: a first and a second side aligned to a firstand a second long edge, respectively, of the first elongated bond pad;and a third and a fourth side aligned to a first and a second long edge,respectively, of the second elongated bond pad, and each of the firstand second elongated bond pads has an extended portion on at least oneside of the contact area.
 2. The package of claim 1, wherein the firstlongitudinal direction is perpendicular to the second longitudinaldirection.
 3. The package of claim 1, wherein the first longitudinaldirection is un-perpendicular to the second longitudinal direction. 4.The package of claim 1, wherein the first elongated bond pad has twoextended portions extending away from the contact area in oppositedirections, and the second elongated bond pad comprises two additionalextended portions extending to opposite sides of the contact area. 5.The package of claim 1, wherein a ratio of the first length to the firstwidth is between about 2 and about
 4. 6. The package of claim 1, whereinthe first package component further comprises: an image sensor array; afirst plurality of elongated bond pads aligned as a first row, whereinthe first elongated bond pad is comprised in the first plurality ofelongated bond pads; and a first plurality of connection lines having asame first length, wherein each of the first plurality of connectionlines electrically connects one of the first plurality of elongated bondpads to image sensors in one column of the image sensor array.
 7. Thepackage of claim 6, wherein the first package component furthercomprises: a second plurality of elongated bond pads aligned as a secondrow not overlapping the first row; and a second plurality of connectionlines having a same second length different from the same first length,wherein each of the second plurality of connection lines electricallyconnects one of the second plurality of elongated bond pads to imagesensors in one column of the image sensor array, and wherein the firstand the second plurality of connection lines are disposed in analternating layout.
 8. The package of claim 6, wherein the first packagecomponent further comprises: a second plurality of elongated bond padsaligned as a second row; and a second plurality of connection lines,wherein each of the second plurality of connection lines electricallyconnects one of the second plurality of elongated bond pads to imagesensors in one column of the image sensor array, and wherein the firstand the second plurality of connection lines are disposed on oppositesides of the image sensor array.
 9. A package comprising: a diecomprising: an array of cells; and a first plurality of elongated bondpads at a surface of the die, wherein each of the first plurality ofelongated bond pads is electrically coupled to one column of the cellsin the array, and wherein the first plurality of elongated bond pads hasfirst longitudinal directions parallel to each other, with each of thefirst plurality of elongated bond pads having a first length in thefirst longitudinal directions, and a first width smaller than the firstlength; a package component comprising: a second plurality of elongatedbond pads at a surface of the package component, wherein each of thesecond elongated bond pads is bonded to one of the first plurality ofelongated bond pads, wherein the second plurality of elongated bond padshas second longitudinal directions parallel to each other, with each ofthe second plurality of elongated bond pads having a second length inthe second longitudinal directions, and a second width smaller than thesecond length, and wherein the second longitudinal directions areun-parallel to the first longitudinal directions, and the firstlongitudinal directions and the second longitudinal directions areparallel to the surface of the die; a first elongated bond pad among thefirst plurality of elongated bond pads; and a second elongated bond padamong the second plurality of elongated bond pads, wherein the firstelongated bond pad and the second elongated bond pad are bonded throughmetal-to-metal bonding, and wherein the first elongated bond padcomprises a first surface comprising a first portion and a secondportion, and the second elongated bond pad comprises a second surfacecomprising a third portion and a fourth portion, with the first portionbonded to the third portion, and the second portion not bonded to thesecond elongated bond pad, and the fourth portion not bonded to thefirst elongated bond pad, wherein the first and the second surfaces havea contact area comprising: a first and a second side aligned to a firstand a second long edge, respectively, of the first elongated bond pad;and a third and a fourth side aligned to a first and a second long edge,respectively, of the second elongated bond pad, and each of the firstand second elongated bond pads has an extended portion on at least oneside of the contact area.
 10. The package of claim 9, wherein the firstlongitudinal directions are perpendicular to the second longitudinaldirections.
 11. The package of claim 9, wherein the first longitudinaldirections are un-perpendicular to the second longitudinal directions.12. The package of claim 9, wherein each of the first plurality ofelongated bond pads has a length and a width, and wherein a ratio of thelength to the width is greater than about
 2. 13. The package of claim 9,wherein the die is comprised in a first wafer comprising a plurality ofdies identical to the die, and wherein the package component iscomprised in a second wafer comprising a plurality of package componentsidentical to the package component.
 14. The package of claim 9, whereinthe die further comprises: a third plurality of elongated bond pads atthe surface of the die, wherein each of the third plurality of elongatedbond pads is electrically coupled to one column of the cells in thearray, and wherein the third plurality of elongated bond pads has thirdlongitudinal directions parallel to each other, and wherein the firstplurality of elongated bond pads is aligned as a first row, and thethird plurality of elongated bond pads is aligned as a second row.
 15. Apackage comprising: a first die; a first bond pad at a surface of thefirst die, wherein the first bond pad has a rectangular top-view shape,and wherein the rectangular top-view shape has a first length extendingin a first direction, and a first width smaller than the first length; asecond die bonded to the first die; and a second bond pad at a surfaceof the second die and bonded to the first bond pad, wherein the secondbond pad has a second length extending in a second directionperpendicular to the first direction, and a second width smaller thanthe second length, and the first length, the first width, the secondlength, and the second width are measured in directions parallel to thesurface of the first die and the surface of the second die, wherein thefirst bond pad and the second bond pad are bonded through metal-to-metalbonding, and wherein the first bond pad comprises a first surfacecomprising a first portion and a second portion, and the second bond padcomprises a second surface comprising a third portion and a fourthportion, with the first portion bonded to the third portion and thesecond portion not bonded to the second bond pad, and the fourth portionnot bonded to the first bond pad, wherein the first and the secondsurfaces have a contact area comprising: a first and a second sidealigned to a first and a second long edge, respectively, of the firstbond pad; and a third and a fourth side aligned to a first and a secondlong edge, respectively, of the second bond pad, and each of the firstand second bond pads has an extended portion on at least one side of thecontact area.
 16. The package of claim 15, wherein the first length isequal to the second length, and wherein the first width is equal to thesecond width.
 17. The package of claim 15, wherein the first die iscomprised in a first un-sawed wafer comprising a first plurality ofdies, and the second die is comprised in a second un-sawed wafercomprising a second plurality of dies.
 18. The package of claim 15further comprising: a first dielectric layer in the first die, wherein atop surface of the first dielectric layer is level with a top surface ofthe first bond pad, and wherein a portion of the second bond pad is incontact with the top surface of the first dielectric layer; and a seconddielectric layer in the second die, wherein a top surface of the seconddielectric layer is level with a top surface of the second bond pad, andwherein a portion of the first bond pad is in contact with the topsurface of the second dielectric layer.
 19. The package of claim 15,wherein the first bond pad has two extended portions extending away fromthe contact area in opposite directions.